In optical communication systems, messages are transmitted by electromagnetic carrier waves at optical frequencies that are generated by sources such as lasers and light-emitting diodes. One preferred device for routing or guiding waves of optical frequencies from one point to another is an optical waveguide. The operation of an optical waveguide is based on the fact that when a light-transmissive medium is surrounded or otherwise bounded by an outer medium having a lower refractive index, light introduced along the axis of the inner medium substantially parallel to the boundary with the outer medium is highly reflected at the boundary, trapping the light in the light transmissive medium and thus producing a guiding effect between channels. A wide variety of optical devices can be made which incorporate such light guiding structures as the light transmissive elements. Examples, without limitation, include planar optical slab waveguides, channel optical waveguides, rib waveguides, optical couplers, optical splitters, optical switches, optical filters, arrayed waveguide gratings, waveguide Bragg gratings, variable attenuators and the like. For light of a particular frequency, optical waveguides may support a single optical mode or multiple modes, depending on the dimensions of the inner light guiding region and the difference in refractive index between the inner medium and the surrounding outer medium.
Organic polymeric materials can be used to construct optical waveguide and interconnect devices such as those given above. However, whereas single mode optical devices built from planar waveguides made from glass are relatively unaffected by temperature, devices made from organic polymers may show a significant variation of properties with temperature. This is due to the fact that organic polymeric materials have a relatively high thermo-optic coefficient (dn/dT). Consequently, a change in temperature causes the refractive index of an optical device made from a polymeric material to change appreciably. This ability to have a change in polymer refractive index due to a temperature change can be used to make active, thermally tunable or controllable devices incorporating light transmissive elements. One example of a thermally tunable device is a 1×2 switching element activated by the thermo-optic effect. In such a device light from an input waveguide may be switched between two output waveguides by the application of a thermal gradient induced by a resistive heater for which the heating/cooling processes occur over the span of one to several milliseconds.
Most polymeric materials, however, contain carbon-hydrogen bonds, which absorb strongly in the 1550 nm wavelength range that is commonly used in telecommunications applications, causing devices made from such materials to have unacceptably high insertion losses. By lowering the concentration of C—H bonds in a material through replacement of C—H bonds with C-D or C-halogen bonds, it is possible to lower the absorption loss at infrared wavelengths. For example, planar waveguides made from fluorinated polyimides and deuterated or fluorinated polymethacrylates have achieved single mode losses of as little as 0.10 dB/cm at 1300 nm and 0.2 bB/cm at 1550 nm. However, it is relatively difficult to make optical devices from these materials. For example, the processes for making such polymeric waveguides typically includes the use of a reactive ion etching process, which is cumbersome and can cause high waveguide loss due to scattering. In addition, deuteration is not an effective means of reducing loss in the 1550 nm wavelength range. Further, fluorinated polyimides and deuterated or fluorinated polymethacrylates can have higher losses on the order of 0.6 dB/cm in the telecommunications window near 1550 nm. Finally, O—H and N—H bonds which may be present in polyinides and polyacrylates contribute strongly to loss at wavelengths near 1310 nm and 1550 nm.
Consequently, in view of the foregoing problems, new polymerizable compositions are sought in which the presence of O—H and N—H bonds is minimal or absent. Further, in view of the foregoing problems encountered using hydrogenated, deuterated and fluorinated polymeric materials, it is also desirable to find new compositions which will not only minimize absorption losses, but will also have a refractive index as high as or higher than the corresponding hydrogenated or fluorinated materials. Organic materials containing sulfur atoms have been found to generally have a higher refractive index than similar compounds that do not contain sulfur atoms. In addition, it has been found that organic materials containing sulfur and chlorine atoms have the desired high refractive indices desired for optical communications devices while maintaining a low C—H count. In particular, it is desirable to prepare novel aromatic vinyl sulfide compounds in which the aromatic ring is highly halogenated